The present invention relates to a process for the manufacture of nitrous oxide by decomposition of ammonium and nitrate ions in an aqueous reaction liquor in a reaction space in which reaction liquor there is maintained a catalysing concentration of chloride ion and strongly acid conditions, nitrous oxide formed by decomposition of ammonium and nitrate ions being withdrawn from the reaction space.
A batch process in which this is achieved, e.g. in the context of removing ammonium nitrate quantitatively from fission product solutions, is described in U.S.A. Pat. No. 3,411,883. However, the process was not rendered continuous or optimalised to render it attractive as a competitor for the conventional process of manufacturing nitrous oxide.
Nitrous oxide, also known as laughing gas, is manufactured commercially by thermally decomposing a melt of pure ammonium nitrate at 250.degree. to 260.degree. C. In that manufacture it is essential that the ammonium nitrate is of special purity. In particular any chlorides must be absent because even at much lower temperatures it is found (even as low as 145.degree. C.) that the presence of traces of chloride ion in a melt of ammonium nitrate results in the formation of a gas containing as much as 70% nitrogen. Moreover, in the anhydrous melt the presence of chloride may give rise to explosions.
In the conventional process the nitrous oxide must be treated to remove impurities, in particular oxides of nitrogen normally by scrubbing with alkaline potassium permanganate solution. This is a wasteful purifying step which results in no useful by-products, and which is based on slow chemical reactions.
It is an object of the present invention to provide a continuous process for the manufacture of nitrous oxide wherein the nitrous oxide can readily be recovered in very pure form, which is very easily regulated and which is advantageous over the prior art in various respects.
In particular the new process can be carried out with industrial grade ammonium nitrate which has not been manufactured in a particularly pure form, a suitable grade being for example, that used in the manufacture of ammonium nitrate fertilizer. It is a comparatively low-temperature process, involving no explosive hazard under normal operating conditions, and for a given plant the throughput can be readily regulated within comparatively wide limits.
The conventional industrial process for the manufacture of nitrous oxide in addition employs a further scrubbing stage with dilute sulphuric acid for the removal of ammonium nitrate fumes and ammonia vapour. This particular scrubbing stage is also found unnecessary in the present process.